The Grumman XF10F-1 Jaguar was a swing wing aircraft which reached the prototype stage and underwent a year of tests but that never entered production.
Work on what would become the XF10F began in 1947. Grumman had been working on their first fighter design, the straight winged F9F Panther since 1946. By this point Grumman was aware that swept wings would probably produce faster aircraft, and on 3 September 1947 submitted their Design 83 to the Navy. On 16 December 1947 the Navy issued a letter of intent to Grumman for the development of the XF9F-2 (the first single engine Nene powered version of the aircraft), and in the same letter also requested an engineering proposal for a swept wing version. In the end the search for a swept wing version of the Panther would produce two designs – the XF10F-1 Jaguar and the confusingly designated F9F Cougar.
The Grumman Design 83 was for an aircraft with a length of 49ft 6in and wing span of 32in 4in. It was to be powered by a single Rolls-Royce Nene engine of 5,000lb thrust, produced under licence in the US as the Pratt & Whitney J42. It had a ‘T’ tail, with the horizontal surfaces at the top of the vertical. The air intakes for the jet engine were in the wing roots. The wings were mid-mounted on the slender circular fuselage. This design was so different to the F9F that on 4 March 1948 it was re-designated as the XF10F-1.
On 7 April 1948 a letter of intent was issued for two prototype XF10F-1s. During the year the design evolved into a very different second version, which became the basis of the prototype. The wings were now high mounted, level with the top of the fuselage. The air intakes were on either side of the lower part of the nose. The horizontal tail surfaces had been moved down to the sides of the rear fuselage. Wing span was down to 29ft 7in, weight was slightly up, and the engine had been upgraded to a 6,500lb thrust Pratt & Whitney J48, a licence built version of the Rolls-Royce Tay.
At the same time Grumman produced a design for a rocket boosted interceptor version of the same design (Design 86). This kept the overall layout of the second version of Design 83, but with a rocket under fuselage and the jet air intakes slightly further up the side of the aircraft.
By April 1949 Grumman had produced a mock-up of the XF10F-1. After the Navy inspected the design they requested a series of changes that would have added too much weight to the aircraft to make it a viable carrier aircraft.
Grumman’s response to this problem was to develop a variable swept wing, or swing wing, version of the design. The advantage of this design is that the wing can move from a straight position, which maximises lift, allowing the aircraft to operate more easily from carrier flight decks and allows for more economical cruising, then moved to the swept back position in flight to allow for higher speed. At the same time they reverted to the original ‘T’ tail.
The Navy was interested in this new design. Grumman officially proposed the idea on 7 July 1949 and on 18 August 1950 was given a letter of intent for twelve XF10F-1s. This was followed by a formal contract for those aircraft on 14 December and an order for another seventy aircraft on 10 February 1951.
Only the first prototype would ever be completed. This aircraft was larger than the original designs, with a length of 55ft 7in, wing span of 50ft 7in when straight or 36ft 8in when swept back. The engine had been changed to a Westinghouse J-40, a new design for a high powered engine with afterburner. This would prove to be one of the greatest weaknesses of the F10F, as the J-40 engine failed after the higher powered versions that were meant for production proved to have a flawed compressor design. To make things worse, the lower powered version that was available didn’t have a working afterburner when the F10F was being tested, which limited its performance. The wing could be swept from 13.5 degrees back to 42.5 degrees (with the most extreme angles meant for carrier storage).
Lateral control was meant to be provided by eight paddle spoilers which were mounted at ninety degrees to the surface of the wing, and could rotate through 180 degrees, from straight up to straight down. Small ailerons were installed to provide ‘feel’ for the pilot as the spoilers were expected to produce very little feedback force to the pilot.
This aircraft was ready by early 1952. Grumman carried out its taxi trials at Bethpage, and then on 16 April 1952 it was flow to Edwards Airforce Base on a C-124. The only man to ever flight the aircraft was the Grumman test pilot Corwin ‘Corky’ Meyer (who also later wrote an excellent book on the aircraft).
After the aircraft arrived at Edwards, a series of further taxi trials were carried out. The tail design proved to make it difficult to take off on the runway. On 19 May 1952 the aircraft was moved to Rogers Dry Lake, where there was enough space for Meyer to get it to 160 knots and finally get into the air. However he was unable to retract the wing slats so speed was limited to 200 knots. Other problems were quickly revealed and after a very careful circuit the aircraft landed after a flight of 16 minutes.
Flight tests revealed that the paddle spoiler system didn’t work. The spoilers produced a great deal of unpredictable feedback forces and caused flutter on most test flights. An attempt to add power controls failed. The full length wing slots also caused problems with lateral control. Luckily the small ailerons provided enough control for the test flights and the paddle spoilers and slots were covered over. However the small ailerons didn’t provide enough control for any significant aerobatics, so the full flight characteristics of the aircraft were never explored.
The aircraft had good directional stability when the wings were straight, but in the swept wing position directional stability was poor and useful test data could only be produced in smooth air. Small horizontal dorsal fins were added on either side of the jet pipe, and this improved stability to an acceptable level.
On the plus side the aircraft did prove that the basic purpose of the swept wings did work. The F10F had a lower stall speed and lower landing speed than the contemporary McDonnell F3H, which had similar wings to the swept back version of the F10F. Indeed the wing sweeping mechanism was one of the few parts of the aircraft that didn’t cause problems.
The biggest problems were with the aerodynamically balanced tail. Grumman attempted to fix this, but eventually had to give up and installed a powered tail from an F9F-6. This change was made for the 29th test flight on 23 April 1953, a year into the test programme, and greatly improved the aircraft’s handling, but by now it was too late. The success of the more conventional swept wing F9F Cougar meant that the more radical F10F was no longer needed and the project was abandoned.
Engine: Westinghouse J-40
Power: 6,700lb normal, 7,400lb military, 10,900lb afterburner
Span: 50ft 7in when straight or 36ft 8in when swept back
Length: 55ft 7in
Height: 16ft 3in
Empty weight: 20,468lb
Maximum take-off weight: 35,370lb (with two 300 gallon wing tanks)
Armament: Four 20mm cannon
Bomb load: Two rocket pods (24 rockets each), two 2,000lb bombs